Planographic printing plates having a bohmite oxide interlayer and process for producing same



United States Patent PLANOGRAPHIC PRINTING PLATES HAVING A BOHMITE OXIDE INTERLAY-ER AND PROCESS FOR PRODUCING SAME Fritz Uhlig, Wiesbaden-Biebrich, Germany, assignor, by mesne assignments, to Azoplate Corporation, Murray Hill, N1].

N0 Drawing. Filed Dec. 27, 1960, 'Ser. No. 78,300 Claims priority, application Germany, Dec. 30, 1959, K 39,555 13 Claims. *(Cl. 96-1) The present invention relates to plates for planographic printing in which aluminum coated with a btihmite layer (Al O -1H O) is used as supporting material for the reproduction layer.

Aluminum used in the preparation of planographic printing plates requires a pretreatment to ensure that the reproduction coating adheres well. Bright aluminum has been mechanically processed by graining machines or by steel brushes or brushes made of plastic materials in order to obtain a suitable supporting material. Light-sensitive coatings do not, however, adhere to material thus pretreated to the desired extent if very long printing runs are to be obtained. Also, cleaning of the aluminum surface with alkaline agents, in some cases followed by etching with nitric acid and a silication treatment with aqueous alkali silicate solutions, i.e., providing the surface with a thin silicate coating, has been practiced. Aluminum treated in this way has the disadvantage that only a few types of coatings, all of them negative working, adhere thereto.

Aluminum has also been treated electrolytically for reproduction purposes. This process, however, becomes very involved, particularly with regard to the current supply, when the material is being treated from a roll in a continuous process and when wide rolls are being treated.

The possibility of aluminum surfaces being coated with a bohmite layer-a special form of aluminum oxide by treatment with water or steam at temperatures of over 75 C. is also known. These aluminum plates coated with bcihmite layers have increased resistance to corrosion; to further increase resistance, lacquers have been applied to the bohmite layers.

Planographic printing plates consisting of an aluminum support and a reproduction coating have now been found which include, between the reproduction coating and the aluminum support, a bohmite layer.

For the preparation of planographic printing plates,

" aluminum plates having a bobmite coating are provided with a reproduction coating by known methods, e.g., immersion, roller application, application to the rotating base material, the coating mix being preferably dissolved in a solvent. The solvent is afterwards removed and aluminum supports coated with an even, homogeneous layer are then obtained, which can be prepared for use as printing plates in accordance with known methods.

The bohmite coating is produced by known methods on commercially available aluminum, in particular in the form of plates, or in the case of continuous processing, in the form of continuous bands.

For this purpose, the aluminum can be introduced into hot water at a temperature over 75 C. or steam, the

temperature being preferably between 80 and 130 C.

The process is advantageously accelerated by the addition of weakly basic agents, preferably organic bases. These are employed in the form of 0.1 to percent solutions, preferably 1-5 percent solutions.

Suitable bases include, in particular, lower primary secondary and tertiary amines, e.g., trimethylamine,

ethylamine, diethylamine, triethylamine, propylamine,

ice

butylamine, isobutylamine, dibutylamine, tributylamine, diisobutylamine, octylamine, and dioctylamine; also piperidine, N-methylpiperidine, morpholine and aminoalcohols such as monoethanol-amine, diethanolamine and triethanolamine, diamines and polyamines such as ethyl ene diamine and triethylene diamine; lower substituted acid amides such as dimethyl formamide and aqueous solutions of ammonia, or mixtures thereof.

According to the nature of the aluminum surface, the temperature employed and the liquid used, the treatment may take several seconds to a number of hours. In general a treatment of 3 seconds to 30 minutes, preferably 10 seconds to 15 minutes, at temperatures of 65 C.- 130 0., preferably to C., with the solvents that are preferably used, namely aqueous solutions of ammonia, ethanolamine or aliphatic diamines, is satisfactory. It is also known that it is advantageous for deionized water of the greatest possible purity to be used and in particular for silicates, the presence of which inhibit the formation of bohmite coatings, to be excluded.

The b'o'hmite layer thus produced is rinsed down with distilled water and dried and can then be coated by hand or by means of suitable coating machines with solutions of the reproduction coatings.

The reproduction coatings for the planographic printing plates of the invention consist preferably of light sensitive organic compounds such as aliphatic and aromatic esters, hydrazides and amides of naphthoquinone diazide sulfonic acids, cinnamal malonic acid, its substitution products and functional derivatives, ortho and paraquinone diazides of benzene, anthracene and of heterocyclic systems, such as quinoline, indazole, benzimidazole, naphthoimidazole, fluorene, and diphenylene oxide; also diazo ketones, unsaturated ketones, ortho and paraimino quinone diazides, derivatives of alkyl nitrona-phthalene sulfonic acids, as well as certain nitroaldehydes, acenaphthenes, nitrones, stilbenes, azides and diazides and high-polymer diazo compounds.

Also, reproduction coatings, such as are used in electrophotography, which have a high electrical resistance in the absence of light, which is reduced by several powers of ten by exposure to light, may be applied, e.g., organic photoconductors of lower and higher molecular weight, if desired in association with resins. Oxadiazoles, imidazolones, triazoles, oxazoles, thiazoles, hydrazones, triazines, polyvinyl carbazoles and polyvinyl oxazoles have proved particularly suitable as photoconductors.

Suitable resins include those with groups conferring alkali-solubility, such as acid anhydrides, carboxylic acid, sulfonic acid, sulfonamide or sul-fonimide groups, e.g., vinyl polymers and vinyl interpolymers, phthalic acid ester resins, maleinate resins, alkyd resins, colophony resins, and polyacrylic acid resins.

The planographic printing plates of the invention have the advantage that practically all known types of light sensitive substances, in particular the diazo compounds, adhere excellently to the bohmite surface and moreover, after the normal processes of exposure under a master and decoating of the image-free parts, which is effected with Weak alkalis or acids, according to the type of reproduction coating used, they produce longer runs in the machines commonly used for offset printing, sometimes several times as long as those obtained with aluminum foils that have been mechanically roughened. The planogra-phic printing plates further have the advantage of being very simple to produce. for, in general, ordinary rolled aluminum can be passed directly into a bath and subjected to the bohmite treatment. Further, the planographic printing plates of the invention, after being exposed and developed, have the advantage that the bohmite. coating imparts to the image-free parts particularly good water-conductivity.

The invention will be further illustrated by reference to the following specific examples:

Example 1 A continuous band of thin untreated rolled aluminum is drawn through a bath containing 2 percent ammonia solution at a temperature of 80 C.; the immersion time is about minutes. It is followed by rinsing with distilled water and drying. One surface of the dried band is then coated in known manner with a 2 percent solution, in ethyleneglycol monomethylether, of naphthoquinone-(1,2)-di-aZide-(2)-5-sulfonic acid ester of 2,3,4- trihydroxy benzophenone. The material is then dried in hot air and cut into suitable sheets.

For preparation of a printing plate, the sensitized side of the foil is exposed to light under a film master and the exposed coating is treated with a cotton pad soaked in a 3 percent trisodium phosphate solution, after which in the parts not affected by light, a yellow image of the master remains. After being [rinsed with water, it .is inked up with printing ink and can be used in a printing machine, direct images corresponding to the master being obtained. Runs about twice as long as those obtained under identical printing conditions with printing plates made from aluminum that has been mechanically roughened are obtained. The reproduction coating has only moderate adherence to silicated aluminum.

Example 2 is removed by rinsing with water and the image parts are inked up with greasy ink. Printing can then be performed in the usual manner. The number of prints obtained is several times that obtained, under comparable conditions, with printing plates made from mechanically roughened aluminum.

Dior triethanol amine or mixtures of ethanol amines can be used instead of the monoethanol amine with equally good results.

Example 3 An aluminum foil is immersed in a bath containing a solution, heated to 90 C., of 3 percent ethylene diamine in pure water. After minutes, the foil is removed from the bath, rinsed with water, and dried. Subsequently, one side of the foil is coated with a 2 percent solution of 4-diazo diphenylamine chloride in glycol monomethylether and dried again.

When the foil has been dried and exposed to light under a diapositive, a positive image of the master is obtained, if the reproduction coating, in the parts affected by light, is removed by Wiping over with a cotton swab soaked in an organic solvent, preferably ethyl acetate. The foil is rinsed with water, and, if desired, wiped over with about 2 percent phosphoric acid, to increase water-acceptance in the image-free parts, and the image parts are then inked up with greasy ink.

Also, a reversed, i.e. positive image of the master can be obtained if the foil is exposed to light under a negative master, e.g. a photographic negative, and the reproduction coating, in the parts not aifected by light, is then removed with percent phosphoric acid or dilute hydrochloric acid. When the foil has been inked up with greasy ink, printing can be performed.

Example 4 An aluminum foil is treated for about 30 minutes with steam for the production of a bdhmite coating. It is dried and coated with a solution of 1.3 percent of 4-diazo diphenylamine chloride and 0.3 percent of polyacrylic acid in ethyleneglycoi monomethylether. After the reproduction coating has been dried and exposed to light under a master, and the .parts unaffected by light Washed away with water, the plate can be inked up with greasy ink and very long printing runs obtained. Reversed images of the master are obtained. The number of good prints is several times that obtained under comparable conditions with printing plates made from mechanically roughened aluminum.

Example 5 An aluminum foil is immersed for about 10 minutes in a bath containing a solution, heated to C., of 1.5 percent diethanol amine and 1.5 percent triethanolamine in pure water. It is dried and then coated with a solution of 2 percent of cinnamylidene furfurylidene acetone in methyl ethyl ketone. After drying and exposure to light behind a master, removal with 5 percent phosphoric acid of the parts unaifected by the light, a reversed image of the master is obtained which, after inking up with greasy ink, can be used in a printing machine in the usual way.

Example 6 A continuous band of aluminum is treated, as described in Example 1, for the production of a bohmite coating, dried, and then coated with a 32 percent aqueous solution of 4,4'-diazidostilbene-2,2'-disulfonic acid. After drying, exposure to light under a master, and development with water, a reversed image of the master is obtained from which, after inking up with greasy ink, prints can be obtained in a suitable printing machine.

Example 7 An aluminum foil is treated, as described in Example 1, for the production of a bohmite layer, dried, and then coated with a 1.5 percent solution of N-(4'-methyl-benzene 1'-sulfonyl) imino (1) 2,5 diethoxy benzo quinone (1,4) diazide 4 in ethyleneglycol monomethyl ether. When the coating has been dried and exposed to light under a master, the image surface wiped over with about 1 percent trisodium phosphate solution, rinsed with water, and inked up with greasy ink, printing can be done in the usual way. Prints that are a reversed image of the master are obtained.

Example 8 An aluminum foil is treated for the production of a bdhmite layer, as described in Example 1, dried, and then coated with a 1.5 percent solution of 2,2 -fbis (naphthoquinone (1,2) diazide (2) sulfonyloxy (5) )-dinaphthyl-(l,1)-methane in ethyleneglycol monomethylether. When the coating has been dried and exposed to light under a film master, the image-surface wiped over with about 5 percent trisodium phosphate solution, rinsed with water, and inked up with greasy ink, prints can be made in a printing machine, direct images corresponding to the master being obtained.

If a photographic negative is used as master and the light sensitive coating is removed with an organic solvent, e.g. carbon tetrachloride, in the parts not affected by the light, after the plate has been rinsed with water and made Water-conductive by Wiping over with dilute phosphoric acid, a reversed image of the master is obtained, which after inking up with greasy ink, can be used for printing in an offset machine.

The printing run obtained with a printing plate thus produced is several times that possible with a printing plate prepared by applying the same light sensitive coating to mechanically roughened aluminum.

Example 9 One part by weight of 2,5-bis-(4'-diethyl-amino-phenyl- (l)-1,3,4-oxadiazole, 0.8 part by weight of a styrene interpolymer containing carboxyl groups, with a specific gravity of 1.26-1.28 and a decomposition temperature ranging from 200 to 240 C. and 0.003 part by weight by Rhodamine B extra (Schultz Farbstofftabellen, 7th edition, vol. I, No. 864) are dissolved in 30 parts by volume of ethyleneglycol monomethylether and the solution is coated upon an aluminum foil which has been treated for the production of a bohmite coating, as described in Example 1; it is then dried. For the production of images on the electrocopying material thus prepared, the reproduction coating is charged by means of a corona discharge and then exposed under a master for one second to the light of a 125-watt mercury lamp. The electrostatic image of the master thereby produced is made visible by dusting over with a resin powder colored with carbon black and fixed by heating to 150 0, thereby being rendered resistant to abrasion. For the preparation of the printing plate, the electrocopy is wiped over with a solution consisting of 30 parts of methanol, 20 parts of glycerine, and 35 parts of ethyleneglycol. It is rinsed with water and then treated with an about 0.5 to 5 percent aqueous phosphoric acid solution. After the plate has been inked up with greasy ink, prints can be made in an offset machine in the usual manner, direct images corresponding to the master being obtained.

Example 10 A continuous band of thin untreated rolled aluminum is drawn through a bath containing clear boiling water, the immersion time being to 30 seconds, and it is then dried. Subsequently, the band is coated on one side in known manner with a 1.5 percent solution of 1-((4- methyl benzene 1' sulfonyl) imino) 2 (2",5 dimethylphenyl amino sulfonyl) benzoquinone (1,4)-diazide-(4) in ethyleneglycol monomethylether, dried with hot air and cut into sections.

For the preparation of a printing plate, the side of the aluminum foil provided with the reproduction coating is exposed under a negative, transparent master and then treated with a cotton pad soaked in a 3 percent (approx) solution of trisodium phosphate and rinsed with water. A yellow-colored (reversed) image of the master used adheres to the portions struck by light. After inking with greasy ink, the foil may be set up in a printing machine and used for printing.

It will be obvious to those skilled in the art that many modifications are made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. Light-sensitive material comprising an aluminum hase having a Bohmite oxide layer of the formula Al O -H O thereon, and a light-modifiable reproduction coating on the oxide layer.

2. Light-sensitive material according to claim 1 in which the reproduction coating includes a quinone diazide sulfonic acid ester.

3. Light-sensitive material according to claim 1 in which the reproduction coating includes a light-sensitive oxadiazole,

4. A process for making a printing plate which comprises exposing a light-modifiable reproduction coating, supported on an aluminum base having a Bohmite oxide layer of the formula Al O -H O thereon, to light under a master, and treating the exposed coating with a developing solution.

5. A process according to claim 4 in which the reproduction coating includes a quinone diazide sulfonic acid ester.

6. Light-sensitive material according to claim 1 in which the reproduction coating includes a high polymer diazo compound.

7. Light-sensitive material according to claim 1 in which the reproduction coating includes a light sensitive organic compound.

8. A process according to claim 4 in which the reproduction coating includes a high polymer diazo compound.

9. A process according to claim 4 in which the reproduction coating includes a light sensitive organic compound.

10. A process for making a printing plate which comprises exposing an electrostatically charged lightmodifiable reproduction coating, supported on an aluminum base having a bohmite oxide layer of the formula Al O -H O thereon, to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the non-image areas.

11. A process according to claim 10 in which the reproduction coating includes a light-sensitive oxadiazole.

12. A process according to claim 10 in which the reproduction coating includes an organic photoconductor.

13. A process according to claim 10 in which the reproduction coating includes a resin.

Foundation, New York, 1952, pp. 92-125 and 155.

Tory: Photolithography, Graphic Arts, monthly, Chicago, 1953, pp. 183-184.

Uhlig: Corrosion Handbook, John Wiley, and Sons, Inc., New York, 1948, page 617.

Wernick: Metal Finishing, August 1956, pp. 53-59.

NORMAN G. TORCHIN, Primary Examiner.

PHILIP MANGAN, ABRAHAM H. WINKELSTEIN,

Examiners. 

10. A PROCESS FOR MAKING A PRINTING PLATE WHICH COMPRISES EXPOSING AN ELECTROSTATICALLY CHARGED LIGHTMODIFIABLE REPRODUCTION COATING, SUPPORTED ON AN ALUMINUM BASE HAVING A BOHMITE OXIDE LAYER OF THE FORMULA AL2O3.H2O THEREON, TO LIGHT UNDER A MASTER, DEVELOPING THE RESULTING IMAGE WITH AN ELECTROSCOPIC MATERIAL, FIXING THE IMAGE, AND HYDROPHILIZING THE NON-IMAGE AREAS.
 12. A PROCESS ACCORDING TO CLAIM 10 IN WHICH THE REPRODUCTION COATING INCLUDES AN ORGANIC PHOTOCONDUCTOR. 